The present invention relates to a new and improved method of treating a continuously cast strand formed of stainless steel, wherein the strand is withdrawn by rolls, cut and heated for further processing.
Continuously cast strands formed of stainless steel often have oscillation or ripple marks and surface flaws or defects, such as, for instance, slag inclusions. During the subsequent rolling operations, for instance of the slab into a hot band or strip, there occur surface flaws or defects, such as shell or sliver, which appear in the form of small surface cracks or fissures. The problem is particularly acute in the case of hot bands or strip which are fabricated from austenitic stainless steel. An important factor contributing to this problem is the necessity of pronounced grinding of the slab for surface rectification. Due to such surface grinding there is also ground a very thin, fine grained marginal zone or surface layer, which has been formed during the continuous casting process, with the result that there is exposed the coarse columnar structure within. During subsequent heat treatment in a reheating furnace oxygen and sulphur penetration of the product may occur along the grain or columnar boundaries. This ultimately leads to surface break-up or to shell-sliver formation owing to the insufficient hot ductility and to large grinding losses during the treatment of the rolled product.
With non-stainless steels there are known to the art processes in order to eliminate the liquation and/or porosity at the center of a continuously cast strand by thickness reduction at the region of final solidification. Furthermore, there are known processes which deform the strand in the continuous casting installation or immediately following the same in order to reduce the cross-section or for smoothing the strand surface. In this way, starting from an initial cross-section it is possible to directly produce different desired final cross-sections while utilizing the casting heat present within the strand.